Sealed contact reed switch having contoured reeds



APril 25, 1967 K. F. BRADFORD 3,316,513

SEALED CONTACT REED SWITCH HAVING CONTOURED REEDS Filed Jan. 5, 1966FIG. 2

WEI/A lNl EA/TOR A. E BRADFURD ATTORA/EV United States Patent 3,316,513SEALED CONTACT REED SWITCH HAVING CONTQURED REEDS Kenneth F. Bradford,Murray Hill, N..l., assignor to Bell Telephone Laboratories,Incorporated, New York,

N.Y., a corporation of New York Filed Jan. 3, 1956, Ser. No. 518,044 6Claims. (Cl. 335-154) This invention relates to switching devices whichare sensitive to variations in contact resistance and pertainsespecially to switches of the sealed contact reed type.

It is a general object of this invention to increase the stability ofcontact resistance in such devices.

A sealed contact reed switch typically comprises a source of magneticflux, a vessel, and a pair of contacts or reeds. The reeds aremagnetically responsive, and they are sealed in the walls of the vesselas cantilevers with their free ends overlapping and spaced from oneanother by an air gap. When magnetic flux from the source is applied,the reeds come together to establish a continuous electrical path andwhen the magnetic flux is removed, they spring apart to interrupt theelectrical path. While these switches are highly reliable in amechanical sense, they are susceptible to variations in contactresistance.

Contact resistance is the electrical resistance appearing between theopposing faces of the reeds after they have come together, and it isdirectly related to the microscopic mechanical connections joining thetwo reeds. In most switching applications high contact resistance isundesirable.

Reed switches having an initially low contact resistance are readilymade by plating the contact ends of the reeds with various well-knownmaterials. In most applications, however, the contacts are subject toarcing and pitting occurs. As a result, the plating material breaks downand the mechanical connection between the reeds is changed, therebychanging the contact resistance. Although most changes result inincreased contact resistance, it is possible that reduced contactresistance could also occur. In either event, however, the contactresistance becomes unstable.

Accordingly, it is a specific object of this invention to minimizechanges in contact resistance during operation.

It is another specific object of this invention to concentrate pittingof the contacting surfaces in a particular area.

According to one feature of this invention, the contacting ends of thereeds are contoured to have two ribs separated by a web.

In accordance with another feature of this invention, the contactingsurfaces of the two reeds are out of parallel with each other.

In one embodiment of this invention, two spaced-apart and overlappingmagnetic reeds are sealed in opposite ends of a glass tube with bothoverlapping ends slightly out of parallel with each other. Theoverlapping end of one reed is contoured to have two ribs separated by aweb. With this arrangement, the rib closest to the other reed makescontact first and thus sustains all arcing damage, while the ribfurthest from the other reed makes contact in a circuit already closedand consequently suffers no arcing damage. As a result, the contactresistance between the latter rib and the other reed remainssubstantially unchanged from operation to operation.

Other objects and features of this invention will be readily apparentfrom the following detailed description when taken in conjunction withthe drawing in which:

FIG. 1 is an elevation view of a reed switch having portions broken awayto show the overlapping reeds sealed therein;

FIG. 2 is a section view taken along line 2--2 of the reed switch shownin FIG. 1 and shows the configuration of two overlapping reeds made inaccordance with this invention; and

FIG. 3 is an enlarged view of the contoured end portion of a reedillustrated in FGS. 1 and 2 and shows in detail the two ribs and theconnecting web.

A sealed contact reed switch 10 is shown in FIG. 1. The switch 10comprises a vessel 11, two flat overlapping and spaced-apart reeds 12and 13, and a coil 14. The vessel ll is conveniently made of glass,while the reeds 12 and 13 are made of a ferromagnetic material such as52- Alloy. In addition, the reeds have cross-sections thin enough andwide enough to all-ow relatively easy torsional movement.

As shown in FIG. 2, the overlapping ends of the reeds l2 and 13 arecontoured. Moreover, the two reeds are sealed in the vessel 11 so as tobe slightly out of parallel with each other.

One or both of the reeds of the overlapping ends of the reeds can becontoured. Because it is easier to contour all of the reeds when theyare made, however, in the embodiment illustrated both reeds arecontoured. Because both reeds are contoured in the same manner, adescription of one suflices to describe the other.

The cont-our of the reed 13 is shown in detail in FIG. 3. Specifically,the end portion thereof includes two ridges or ribs 15 and 16 and a web17. The ribs 15 and 16 are raised from and separated by the web 17. Inthe embodiment shown, the end portion of the reed 13 has been formed sothat the two ribs 15 and 16 are substantially parallel. While thisarrangement is preferred, others are equally good; the important thingbeing that the end of the reed 13 include two raised edges.

In operation the out of parallel end portions of the reeds 12 and 13 areattracted when the coil 14 is energized. Because the rib 15 is closestto the reed 12, it makes contact first. Thereafter, the reed 13 twistsand the rib 16 engages the reed 12. Consequently, both the rib 15 andthe rib 16 engage the reed 12.

Any arcing during closure occurs between the rib 15 and its counterparton the reed 12. Thus, when the rib 16 engages the reed 12, theelectrical potential between the two is substantially reduced. As aconsequence, the rib l6 suffers little if any arcing damage. Because therib l6 suitors little or no arcing damage, practically no pitting occursand the contact resistance between the rib i6 and the reed 12 remainsstable, operation after operation.

The following table contains data comparing the failure rate of reedswitches containing contoured reeds with reed switches containinguncontoured reeds. For the purposes of the tests, failure was deemed tohave occurred when the total contact resistance in the switch beingtested exceeded .150 ohm.

Percentage of Switch Failures Number of Operations (in millions)Uncontoured Contoured other embodiments within the scope of theinvention will readily occur to others skilled in the art.

What is claimed is:

1. In a switching device sensitive to variations in contact resistance,the combination comprising:

a sealed vessel;

a first contact sealed in said vessel as a cantilever and having a flatfree end;

a second contact for engaging said first contact to open and close anelectrical path, said second contact being sealed in said vessel as acantilever and having a flat free end overlapping and spaced from theflat free end of said first contact, the fiat free end of said secondcontact including two ribs separated by a web, said two ribs forengaging the flat free end of said first contact one after the other andbeing disposed along the long axis of said first contact and one of saidfirst and second contacts being out of parallel with the other wherebythe order in which said two ribs engage said first contact remains fixedand the first rib to engage said first contact electrically connectssaid first and second contacts and carries and extinguishes anyelectrical are appearing between said first and second contacts and thelast rib to engage said first contact is not subject to any electricalarc and establishes a connection having a stable contact resistancebetween said first and second contacts.

2. In a switching device sensitive to variations in contact resistance,the combination comprising:

a sealed vessel;

and first and second contacts for interacting with each other to openand close an electrical path, said first and second contacts beingsealed in said vessel as cantilevers and having free ends overlappingand spaced from each other by an air gap, one of said free endsincluding two raised portions separated by a web and one of said firstand second contacts being out of parallel with the other whereby saidtwo raised portions engage the other free end one after the other in afixed sequence.

3. The combination in accordance with claim 2 wherein the other of saidfree ends includes two raised portions separated by a web.

4. In a switching device sensitive to variations in contact resistancethe combination comprising:

a sealed vessel;

a first contact sealed in said vessel as a cantilever and having a freeend;

a second contact for engaging said first contact, said second contactbeing sealed in said vessel as a cantilever and having a free endoverlapping and spaced from the free end of said first contact, the freeend of said second contact including two separate raised edges joined bya web for engaging the free end of said first contact one after theother in a fixed sequence.

5. In a switching device sensitive to variations in contact resistancethe combination comprising:

a sealed vessel;

21 first contact sealed in said vessel as a cantilever and having a freeend;

a second contact for engaging said first contact, said second contactbeing sealed in said vessel as a cantilever and having a free endoverlapping and spaced from the free end of said first contact, the freeend of said second contact including two separate raised edges forengaging the free end of said first contact one after the other in afixed sequence, and the free ends of said first and second contactsbeing out of parallel.

6. In a switching device sensitive to variations in conresistance thecombination comprising:

a sealed vessel;

a first contact sealed in said vessel as a cantilever and having afree'end;

a second contact for engaging said first contact, said 7 second contactbeing sealed in said vessel as a cantilever and having a free endoverlapping and spaced from the free end of said first contact, the freeend of said second contact including two separate raised edges joined bya web for engaging the free end of said first contact one after theother in a fixed sequence, and the free ends of said first and secondcontacts being out of parallel.

References Cited by the Examiner UNITED STATES PATENTS 9/1949 Curtis20087 4/1956 Meloni et al. 2(lO-l 16 200-116 2,481,003 2,740,8703,068,335 12/1962 Gregg References Cited by the Applicant UNITED STATESPATENTS 4/ 1955 Brewer. 12/1963 Spooner et al.

7/ 1964 Wagar.

1. IN A SWITCHING DEVICE SENSITIVE TO VARIATIONS IN CONTACT RESISTANCE,THE COMBINATION COMPRISING: A SEALED VESSEL; A FIRST CONTACT SEALED INSAID VESSEL AS A CANTILEVER AND HAVING A FLAT FREE END; A SECOND CONTACTFOR ENGAGING SAID FIRST CONTACT TO OPEN AND CLOSE AN ELECTRICAL PATH,SAID SECOND CONTACT BEING SEALED IN SAID VESSEL AS A CANTILEVER ANDHAVING A FLAT FREE END OVERLAPPING AND SPACED FROM THE FLAT FREE END OFSAID FIRST CONTACT, THE FLAT FREE END OF SAID SECOND CONTACT INCLUDINGTWO RIBS SEPARATED BY A WEB, SAID TWO RIBS FOR ENGAGING THE FLAT FREEEND OF SAID FIRST CONTACT ONE AFTER THE OTHER AND BEING DISPOSED ALONGTHE LONG AXIS OF SAID FIRST CONTACT AND ONE OF SAID FIRST AND SECONDCONTACTS BEING OUT OF PARALLEL WITH THE OTHER WHEREBY THE ORDER IN WHICHSAID TWO RIBS ENGAGE SAID FIRST CONTACT REMAINS FIXED AND THE FIRST RIBTO ENGAGE SAID FIRST CONTACT ELECTRICALLY CONNECTS SAID FIRST AND SECONDCONTACTS AND CARRIES AND EXTINGUISHES ANY ELECTRICAL ARC APPEARINGBETWEEN SAID FIRST AND SECOND CONTACTS AND THE LAST RIB TO ENGAGE SAIDFIRST CONTACT IS NOT SUBJECT TO ANY ELECTRICAL ARC AND ESTABLISHES ACONNECTION HAVING A STABLE CONTACT RESISTANCE BETWEEN SAID FIRST ANDSECOND CONTACTS.